The theorem that international trade in commodities will ensure that factor prices are equalized across countries. In the Heckscher–Ohlin model, which explains inter-industry trade, countries specialize in the production and export of goods whose production requires relatively large inputs of their more plentiful factors of production, and import part or all of their requirements of goods requiring large inputs of their scarcer factors. Imports of goods intensive in scarce factors lower the demand for them, and therefore their factor prices. Exports raise the demand for, and thus the price of, abundant factors. If there are no transport costs and no restrictions on international trade, complete factor price equalization results. In the presence of transport costs and trade barriers, trade tends merely to reduce international factor price differences.